What is tinnitus? Good question. I didn't know about it until I got it. It is constant ringing of ear that doesn't stop ... ever.
I've had mine for about 5 years now. It's constant high pitched flat sound in my right ear. It's just above human voice frequencies so it doesn't affect hearing people talk that much. Sometimes hours can go that I don't notice it, but when I do, it gets louder and bothers again. This is specially fun at nighttime.
What causes it? Usually some trauma that damages ear. In most cases loud noise. What caused mine? I have no clue. I've never been big on rock-concerts, listening to music really loud or other forms of ear-torture. There are some medical conditions that can cause tinnitus too but most doctors I've met are really reluctant to have anything to do with it.
In this time and age of spacetechnology and understanding of human body and genome one could think there is something to do about tinnitus ... one would be dead wrong. Sure there is all sorts of things that help tolerate tinnitus better (hypnosis, mental exercises) but not an actual cure. This plus quite desperate people with ringing ears leaves really nice living space for all sorts of scams. There are homeopathic "medicines" that's supposed to work and all that non-sense. I would like to trust in science instead of placebo effect.
One of the most succesful ways to ease my being ... specially when trying to sleep ... is counternoise. I bought this radio that plays MP3s and have been experimenting with different noises for over a year now. Textbook solution is whitenoise/pinknoise. In my case it had to be played quite loud before it did anything for me. First sound that worked for me was noise of dryer going on. Nice humming sound with regular soft thumbing sound was pretty good. Sound of shower was even better. Problem was that voice of running water worked it's magic with human bladder and running between bed and bathroom all night wasn't working either. At the moment I am listening to sound of rain on top of tent all night long. Soothing and takes attention away from tinnitus quite well.
Seems that tinnitus is quite personal and different things work with different people. I would love to hear from you if you happen to know anything that have helped someone.